17,077 research outputs found
Recovery of continuous wave squeezing at low frequencies
We propose and demonstrate a system that produces squeezed vacuum using a
pair of optical parametric amplifiers. This scheme allows the production of
phase sidebands on the squeezed vacuum which facilitate phase locking in
downstream applications. We observe strong, stably locked, continuous wave
vacuum squeezing at frequencies as low as 220 kHz. We propose an alternative
resonator configuration to overcome low frequency squeezing degradation caused
by the optical parametric amplifiers.Comment: 9 pages, 4 figure
Strong practical stability based robust stabilization of uncertain discrete linear repetitive processes
Repetitive processes are a distinct class of 2D systems of both theoretical and practical interest whose dynamics evolve over a subset of the positive quadrant in the 2D plane. The stability theory for these processes originally consisted of two distinct concepts termed asymptotic stability and stability along the pass respectively where the former is a necessary condition for the latter. Stability along the pass demands a bounded-input bounded-output property over the complete positive quadrant of the 2D plane and this is a very strong requirement, especially in terms of control law design. A more feasible alternative for some cases is strong practical stability, where previous work has formulated this property and obtained necessary and sufficient conditions for its existence together with Linear Matrix Inequality (LMI) based tests, which then extend to allow control law design. This paper develops considerably simpler, and hence computationally more efficient, stability tests that extend to allow control law design in the presence of uncertainty in process model
Gradient Echo Quantum Memory for Light using Two-level Atoms
We propose a quantum memory for light that is analogous to the NMR gradient
echo. Our proposal is ideally perfectly efficient and provides simplifications
to current 3-level quantum memory schemes based on controlled inhomogeneous
broadening. Our scheme does not require auxiliary light fields. Instead the
input optical pulse interacts only with two-level atoms that have linearly
increasing Stark shifts. By simply reversing the sign of the atomic Stark
shifts, the pulse is retrieved in the forward direction. We present analytical,
numerical and experimental results of this scheme. We report experimental
efficiencies of up to 15% and suggest simple realizable improvements to
significantly increase the efficiency.Comment: 4 pages, 4 figure
Pulsed squeezed light: simultaneous squeezing of multiple modes
We analyze the spectral properties of squeezed light produced by means of
pulsed, single-pass degenerate parametric down-conversion. The multimode output
of this process can be decomposed into characteristic modes undergoing
independent squeezing evolution akin to the Schmidt decomposition of the
biphoton spectrum. The main features of this decomposition can be understood
using a simple analytical model developed in the perturbative regime. In the
strong pumping regime, for which the perturbative approach is not valid, we
present a numerical analysis, specializing to the case of one-dimensional
propagation in a beta-barium borate waveguide. Characterization of the
squeezing modes provides us with an insight necessary for optimizing homodyne
detection of squeezing. For a weak parametric process, efficient squeezing is
found in a broad range of local oscillator modes, whereas the intense
generation regime places much more stringent conditions on the local
oscillator. We point out that without meeting these conditions, the detected
squeezing can actually diminish with the increasing pumping strength, and we
expose physical reasons behind this inefficiency
Gradient echo memory in an ultra-high optical depth cold atomic ensemble
Quantum memories are an integral component of quantum repeaters - devices
that will allow the extension of quantum key distribution to communication
ranges beyond that permissible by passive transmission. A quantum memory for
this application needs to be highly efficient and have coherence times
approaching a millisecond. Here we report on work towards this goal, with the
development of a Rb magneto-optical trap with a peak optical depth of
1000 for the D2 transition using spatial and temporal
dark spots. With this purpose-built cold atomic ensemble to implement the
gradient echo memory (GEM) scheme. Our data shows a memory efficiency of % and coherence times up to 195 s, which is a factor of four greater
than previous GEM experiments implemented in warm vapour cells.Comment: 15 pages, 5 figure
Time- and frequency-domain polariton interference
We present experimental observations of interference between an atomic spin
coherence and an optical field in a {\Lambda}-type gradient echo memory. The
interference is mediated by a strong classical field that couples a weak probe
field to the atomic coherence through a resonant Raman transition. Interference
can be observed between a prepared spin coherence and another propagating
optical field, or between multiple {\Lambda} transitions driving a single spin
coherence. In principle, the interference in each scheme can yield a near unity
visibility.Comment: 11 pages, 5 figure
Squeezing and entanglement delay using slow light
We examine the interaction of a weak probe with atoms in a lambda-level
configuration under the conditions of electromagnetically induced transparency
(EIT). In contrast to previous works on EIT, we calculate the output state of
the resultant slowly propagating light field while taking into account the
effects of ground state dephasing and atomic noise for a more realistic model.
In particular, we propose two experiments using slow light with a nonclassical
probe field and show that two properties of the probe, entanglement and
squeezing, characterizing the quantum state of the probe field, can be
well-preserved throughout the passage.Comment: 2 figures; v2: fixed some minor typographical errors in a couple of
equations and corrected author spelling in one reference. v3: Added three
authors; changed the entaglement definition to conform to a more accepted
standard (Duan's entanglement measure); altered the abstract slightly. v4:
fixed formatting of figure
Unification of bulk and interface electroresistive switching in oxide systems
We demonstrate that the physical mechanism behind electroresistive switching
in oxide Schottky systems is electroformation, as in insulating oxides.
Negative resistance shown by the hysteretic current-voltage curves proves that
impact ionization is at the origin of the switching. Analyses of the
capacitance-voltage and conductance-voltage curves through a simple model show
that an atomic rearrangement is involved in the process. Switching in these
systems is a bulk effect, not strictly confined at the interface but at the
charge space region.Comment: 4 pages, 3 figures, accepted in PR
Photon number discrimination without a photon counter and its application to reconstructing non-Gaussian states
The non-linearity of a conditional photon-counting measurement can be used to
`de-Gaussify' a Gaussian state of light. Here we present and experimentally
demonstrate a technique for photon number resolution using only homodyne
detection. We then apply this technique to inform a conditional measurement;
unambiguously reconstructing the statistics of the non-Gaussian one and two
photon subtracted squeezed vacuum states. Although our photon number
measurement relies on ensemble averages and cannot be used to prepare
non-Gaussian states of light, its high efficiency, photon number resolving
capabilities, and compatibility with the telecommunications band make it
suitable for quantum information tasks relying on the outcomes of mean values.Comment: 4 pages, 3 figures. Theory section expanded in response to referee
comment
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